The present invention relates to a method for reduction of pollution emitted from combustion chambers. More specifically the invention relates to a method for reduction of pollution emitted from combustion chambers as in diesel and gasoline engines in motor vehicles and chambers in which combustion of gaseous, liquid and/or solid fuel takes place. The reduction of pollution is achieved by rhodium, platinum and rhenium as catalysts.
It is well established that the major pollutants produced by combustion chambers are soot (carbon), carbon monoxide, and oxides of nitrogen hereinafter referred to as NO.sub.x.
In recent years attempts were made to reduce pollution in various ways by using platinum-group catalysts but the results were only partially successful. In addition rhenium was used in order to increase the octane number in gasoline instead of using lead.
It became apparent that as combustion temperatures rose, soot and CO decreased but at the same time NO.sub.x increased, the latter being an undesirable result. On the other hand, if the combustion temperature is decreased, the NO.sub.x indeed drops, but the amount of soot and CO increases, and simultaneously the efficiency of the fuel utilization drops.
Attempts were made to use platinum as a catalyst for oxidizing the undesired carbon and the CO to CO.sub.2 in combustion chambers. (See U.S. Pat. No. 4,295,816). This patent discloses use of the entire Platinum group for oxidation purposes, but refers primarily to platinum. Over the last decade platinum has been used as a homogeneous catalyst to oxidize C+CO to CO.sub.2 in both engines and furnaces.
However, the problem remained as to how to reduce the NO.sub.x chemically to the gases N.sub.2 and O.sub.2, this being an exothermic reaction.